This invention relates to silicon-containing (meth)acrylate monomers which are useful as coupling agents or adhesion promoters in free radically curable compositions such as UV curable and peroxide curable (meth)acrylate-based coating Compositions.
In the past 20 years, radiation curing has become more and more popular since it provides low or zero volume emission and high productivity. This new technology has been widely used in coatings, inks and adhesives. Radiation curable compositions are typically mixtures of monomers, oligomers, photoinitiators, or additives which are applied to the substrates and cured in place via ultraviolet light. The adhesion between the substrates and the cured compositions varies from system to system. Various additives have been used to improve adhesion. Silane agents have been widely used to improve adhesion in traditional coatings and composites based on epoxy chemistry. However, the application and selection of silane agents depends on cure mechanisms. In the radiation curable case, only one compound, gamma-methacryloxypropyl trimethoxysilane, is compatible with the cure mechanism and available.
Gamma-methacryloxypropyl trimethoxysilane monomer is a well known commercially available coupling agent for bonding coatings to substrates. The coupling agent is mixed with other copolymerizable monomers such as (meth)acrylates, i.e., acrylates, methacrylates, or mixtures thereof, and the mixture of monomers is applied to a surface and cured.
The methacryloxypropyl trimethoxysilane coupling agent of the prior art is prepared from allylmethacrylate, a volatile and odorous compound. The presence of the allylmethacrylate starting material along with the methacryloxypropyl trimethoxysilane monomer coupling agent also causes odor problems with the cured coatings. Other silane-based coupling agents are available, but are mainly directed to two-part, non-(meth)acrylate systems. See Waldman, Silane Coupling Agents Improve Performance, Modern Paints and Coatings, February, 1996.
PCT publication WO 96/12749 of May 2, 1996 shows silane oligomers and radiation curable coating compositions for optical fiber coating. The silane oligomers are high in molecular weight (500-11,000) and a high level of silane oligomer is needed, typically about 5-99% of the coating composition. These silane oligomers are typically prepared based on urethane chemistry and urethane linkage.
Derwent abstract 95-225640/30 relating to DE-4416857 of Jun. 29, 1995 shows hydrolysable and polymerisable silane(s) useful in coating, adhesive, and moulding compositions and composites prepared from reactive silane and unsaturated compound and polycondensed to hetero polysilicic acid compound or polymerized. These silanes have carboxylic acid functional groups for use in the radiation-hardenable binders. These silane agents are prepared from hydroxy containing compounds and acid anhydride containing silanes.
It is an object of this invention to provide coupling agents which have reduced volatility and odor.
It is another object to provide coupling agents which match the adhesion performance of the prior coupling agents, but avoid the volatility and odor problems.
A further object is to provide improved UV curable coating compositions which have reduced volatility and odor.
These objects, and others as will become apparent from the following disclosure, are achieved by the present invention which comprises in one aspect compounds of the formula 
wherein
R1=H, CH3 
R2=H, CH3, CH2CH3, or CH2CH2CH3 
n=1-10
X=halogen, (C1-C6) alkyl, (C1-C6) alkoxy, or aromatic radical, wherein each of the three X substituents can be the same or different.
In another aspect the invention comprises a method of making such compounds of formula I comprising reacting an alkoxylated allyl(alk)acrylate of the formula 
with a silane of the formula
HSiX3xe2x80x83xe2x80x83(V)
in the presence of a transition metal catalyst.
In another aspect the invention comprises the use of the new monomer compounds in coating and adhesive compositions; the resulting coating compositions, and coated articles.
The novel monomer compounds are the reaction product of a silane of the formula
HSiX3xe2x80x83xe2x80x83(V)
and an alkoxylated(alk)acrylate of the formula 
in the presence of a transition metal catalyst.
Suitable silanes of formula V include trichlorosilane, tribromosilane, trifluorosilane, trimethoxsilane, triethoxysilane, trimethylsilane, and triphenylsilane. The preferred silane is trimethoxysilane.
Suitable alkoxylated(alk)acrylates are the reaction product of alkoxylated allyl alcohol and (meth)acrylic acids. The alkoxylated allyl alcohols are prepared by reacting alkylene oxide with allyl alcohol. Suitable alkylene oxides are ethylene oxide, propylene oxide, which is preferred, butylene oxide, and pentylene oxide. The number of alkylene oxide groups, n, can be about 1 to 10, with about 2 to 5 being preferred.
Suitable (meth)acrylic acids are acrylic acid and methacrylic acid, with the latter preferred.
The transition metal catalyst is preferably platinum based, for example, H2PtCl6. Other suitable catalysts are, for example, rhodium-containing compounds.
Preferred compounds of the invention are those of formula I wherein both R1 and R2 are both methyl, n is about 2-5, and X is methoxy.
The monomers of the invention are preferably used in admixture with other unsaturated monomers and the mixture of monomers is applied to a surface of an article and cured to form a coating or adhesive.
The surfaces to which the coating compositions of the invention can be applied include glass, metal, wood, steel, plastic and the like. The new monomers can be used in the same manner as the prior methacryloxypropyl trimethoxysilane monomer with the advantage of imparting lower odor and having reduced volatility to the radiation curable compositions.
The amounts of the various components in the coating compositions are the radiation curable compositions may contain 05-10% of silane of this invention, 0.5-15% of photoinitiator or photoinitiator mixture, and 50-90% of (meth)acrylate monomers, oligomers or monomer/oligomer mixture. The various components can be mixed as in the regular composition and applied to the substrate surface by roller coating, spraying, or any other method. The applied coatings can be cured by irradiation with UV light. Alternatively, the silane agent could be applied first to the substrate followed by regular coating application and curing.